The present invention relates to an information processing unit having a plurality of shared buses and an adaptor (optional board) connected to the shared buses, and particularly to an information processing unit that prevents the shared buses from falling into bottleneck when data is transferred through the buses, thereby enabling the data transfer to be efficiently conducted.
A known example of the efficient data transmission is disclosed in JP-A-7-141285. In this example, a plurality of adaptors are connected to two shared buses, and select an unused bus in order for data to be transferred through the bus. In the reference JP-A-7-141285, when one of a plurality of adaptors that use two shared buses at a time requests for data transfer, the other ones wait for at least one of the two shared buses to become unused.
Another example is disclosed in JP-A-5-204822. In this example, a processor is used to control two shared buses independently, thereby enabling its read cycle and write cycle operations to be made in parallel, that is, data can be efficiently transferred through the shared buses. In this technique, a plurality of modules to be controlled by the processor are connected to the shared buses, and operated to read or write, transferring data to each other. However, the same module does not make read and write operations at a time.
In addition, efficient data transfer can be made by use of fast clock or by expanding data bus. As this bus controlling method, there are known, for example, a bus mediation circuit disclosed in JP-A-7-210498, and a cache coherence control method using an information processing unit described in JP-A-9-198307.
In these conventional method, however, when fast clock is used, the pattern design and electromagnetic wave leaking countermeasure need high-order skill because of high frequency, and are thus troublesome to make. Even when the width of data to be transferred is expanded, data on the shared bus is transferred in one direction during a certain period of time, that is, data cannot be transferred in both directions at a time.